After losing his medical license, Dr. Matthew Thorne, younger brother of crime boss Rupert Thorne and a former colleague of Thomas Wayne and Leslie Tompkins, is forced to peddle his services to his brother and members of his gang. When Rupert insists that Matthew perform his heart surgery, Batman must protect both of them from assassination.

Poison Ivy, after being released from Arkham, has apparently settled for a normal life, married to her psychiatrist and doting on his two children. Batman and Robin are suspicious, however, because semi-sentient plant-like creatures are committing mayhem all over Gotham.